This invention relates to a method for curing membranes with elemental sulfur wherein the membrane comprises a blend of an ethylene/propylene/nonconjugated diene elastomer (EPDM) and an ethylene-containing polymer which combines the properties of durability and seamability and is useful for covering roofs of building structures.
Thermoset EPDM elastomer compositions are very weather-resistant and they are used extensively as roofing membranes. However, the adhesive systems required to bond connecting sheets of the thermoset roofing provide only marginally adequate bond strength and they add significantly to the installation cost of the roofing membranes because of the labor required. The establishment of strong water-tight seams between adjacent sheets of roofing material is, of course, extremely important in such applications. The seams of the connecting sheets are often subjected to high winds, heavy rains, and snow and ice storms and they must be capable of withstanding the stresses generated by such adverse weather conditions. In addition, the seams of the connecting sheets used on flat roofs are further subjected to additional stress from the pooling of water, which often goes through alternating cycles of freezing and thawing. Finally, foot traffic across the roof covered with sheets of thermoset EPDM elastomers also contributes to considerable stress on the seams over the lifetime of the roofing membrane which may exceed 20 years.
Alternatively, thermoplastic EPDM compositions have been proposed for roofing membranes because they can be seamed rapidly by the application of heat and pressure. However, these compositions have not been used successfully because they soften excessively when exposed to direct sunlight during the warm weather months and thus require careful handling during installation and because they lack the toughness of cured sheets. Improving the hot strength of thermoplastic EPDM by blending it with other higher melting polymeric materials is only a partial solution to these problems. Although the hot strength of the blend is adequate for installation of the roofing membrane, the possibility of damage from foot traffic still exists each summer during hot weather.
Thus there is a need in the roofing membrane industry for a durable, heat seamable composition that does not require the application of adhesives containing organic solvents to the edges of the film or membrane to bond or seal the membranes.